Browsing by Author "Cooper, K"

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    The effect of drying rate on the survival of three desiccation-tolerant angiosperm species.
    (Oxford University Press, 1999) Farrant, J; Cooper, K; Kruger, L; Sherwin, H
    The effect of drying rate on the survival of three angiosperm resurrection plants, Craterostigma wilmsii (homoiochlorophyllous), Xerophyta humilis (poikilochlorophyllous) and Myrothamnus flabellifolius (homoiochlorophyllous) was examined. All species survived slow drying, but only C. wilmsii was able to survive rapid drying. C. wilmsii was rapidly able to induce protection mechanisms such as folding of cell walls to prevent mechanical stress and curling of leaves to minimize light stress, and thus survived fast drying. Rapid drying of X. humilis andM. flabellifolius appeared to allow insufficient time for complete induction of protection mechanisms. In X. humilis, there was incomplete replacement of water in vacuoles, the photosynthetic apparatus was not dismantled, plasma membrane disruption occurred and quantum efficiency of photosystem II (FV/FM) did not recover on rehydration. Rapidly dried leaves of M. flabellifolius did not fold tightly against the stem and FV/FMdid not recover. Ultrastructural studies showed that subcellular damage incurred during drying was exacerbated on rehydration. The three species co-occur in environments in which they experience high desiccation pressures. C. wilmsii has few features to retard water loss and thus the ability for rapid induction of subcellular protection is vital to survival. X. humilis and M. flabellifolius are able to retard water loss and protection is acquired relatively slowly. Copyright 1999 Annals of Botany Company.
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    Leaf tensile properties of resurrection plants differ among species in their response to drying.
    (Elsevier, 2009) Hedderson, N; Balsamo, R; Farrant, J; Cooper, K
    Previous studies report that leaf tensile strength (TS) of the desiccation tolerant (resurrection) grass Eragrostis nindensis does not change on drying, but increases in dried desiccation sensitive Eragrostis species. In this paper we tested whether unchanging TS on dehydration is a common feature among 4 resurrection species, Craterostigma wilmsii, Sporobolus stapfianus, Xerophyta humilis and Xerophyta schlecteri, and how this might relate to leaf structure and mechanisms of protection against mechanical stress of drying. Desiccation sensitive controls were Zea mays and Arabidopsis thaliana. Light and transmission electron microscopy of leaves was performed to determine lignification and the nature of subcellular mechanical stabilization. There was a positive correlation between % lignin/unit cross-sectional area and TS of hydrated leaves. Only the grass, S. stapfianus, did not change TS when naturally dried. All others increased in TS when naturally dried, but there was variation among them when flash dried. In S. stapfianus, mechanical stabilization was by both wall folding (mesophyll) and vacuole packaging (bundle sheath) as reported for E. nindensis. This combination may account, in part, for unchanging TS during drying and may be a feature of resurrection grasses. We conclude that leaf tensile properties differ among resurrection plants and are not necessarily affected by protection mechanisms associated with mechanical stress.